Center pivot irrigation systems are well known in the art and are generally comprised of a central source of water about which an elongated radial water distribution pipe rotates. The pipe, which carries a number of sprinklers along its length, is elevated above the ground by a series of support towers which have wheels and therefore travel in large circles about the center pivot point.
The support towers are generally driven by water pressure, by electric motors, or by hydraulic motors. Regardless of the propulsion means, it is critical that the elongate conduit remain in a straight line as it rotates about the center point in order to keep from bending or breaking the conduit. This is accomplished by constantly adjusting the speed of each of the support towers. Obviously, the outermost tower has the furthest distance to travel and therefore must travel the fastest, with each succeeding inward tower traveling slightly slower.
Most systems utilize a "follow the leader" system in which the movement of each tower is controlled by the tower just outward from it. Consider a hydraulically powered center pivot irrigation system having a total of three towers extending from a center pivot. Pivoting is begun by applying hydraulic pressure to one of two hydraulic lines extending to each tower from a central pump. A hydraulic motor at the outermost, or third, tower receives pressure and begins to drive the tower. As this third tower moves forward, the third section of conduit begins to become misaligned with the second section since the second tower has not yet moved. This misalignment is translated into a linear movement by means of a pivot arm or bell crank attached to the outer conduit section which in turn repositions a hydraulic valve on the second tower. Repositioning the second tower hydraulic valve provides hydraulic pressure to the second tower hydraulic motor and it then begins to move. If, for some reason the second tower drive means should fail or the tower should get stuck, the valve moves past the drive position and into a bypass position where fluid bypasses the motor and is diverted back into the return line. This tends to equalize pressure in the two hydraulic lines and all tower movement stops. In order to realign the conduit, the farmer must generally disconnect the valve on the stalled second tower and move it from the bypass position to the neutral position in order to get hydraulic pressure to the outer tower to drive it back into line. When that is accomplished, he must then return to the second tower and reconnect the hydraulic valve.
Direction of rotation of prior art systems is controlled by pressurizing one or the other of the two hydraulic lines extending to the support towers. Speed of movement is a function of the hydraulic pressure supplied to the system.